From: Sandy King (sanking@clemson.edu)
Date: 10/28/01-06:23:15 PM Z
In a previous message I wrote:
>By convention, for both negative and print emulsions, speed is
>determined by >the first maximum black recorded ( or some % of
>maximum black). The number of >steps recorded determines exposure
>scale (ES), or contrast, but has nothing at >all to do with speed.
My mind was obviously wandering when I wrote the above because, as
Dave has pointed out to me,
>Most other literature defines speed relative to Dmin, e.g. speed point
>of negative is usually defined as 0.1+Dmin although ISO defines it slightly
differently, speed point of paper is 0.6 (or 0.7) + Dmin.
He is of course correct. However, since actual printing times are
established by the time needed to print the first maximum black (or
90% of maximum black) it is my opinion that Dmax or 90% of Dmax
should be the step that establishes the printing speed of an
alternative process with any given light source. The overall contrast
of the print will be established by the sensitivity of the process as
determined by the number of steps between Dmax and Dmin (or between
IDMax and IDmin).
If there is any specific reason why it would be better to use the
convention observed for silver papers, i.e, the speed point is 0.6 +
Dmin, instead of Dmax I would be very interested to understand the
logic. I have to say quite frankly that I don't understand the
rationale for the convention and perhaps am missing an important
consideration.
Sandy King
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